Fire alarm system



Aug- 27, l957 R. w. CURTIS ET AL 2,804,610

FIRE: ALARM SYSTEM Filed July s, 195e JE. j. ,f---- /ef l r* YQ-fwd g i I l? L A a 3 f' i 1 f a l I v z Qi 6)- f L 20 INVENToR g 6065 n4 60,6775 5 FIRE ALARM sYsrEM Roger W. Curtis, Bethesda, and Nathan Kaplan, Silver Spring,Md.

Application July 3, 1956, Serial No. 595,806 Claims. (Cl. 34a- 227) (Granted under Title 35, U. S. Code (1952), sec. 266) some system in which an outside powersupply, usually aV battery is required to energize the re alarm, the thermal detector being operative only to energize some sensitive relay as in a thermocouple system, or to establish a circuit from the battery to the lire alarm. In the latter type, an electrode and fused salt combination is most commonly used wherein the salt will establish a conductive path for electricity at some predetermined-increase in temperature, the salt being nonconductive at normal temperatures and up to the predetermined value. In'both types of thermal detection, certain disadvantages attend their use, including a substantial time lag between thev initial predetermined temperature condition and the energization of the alarm, a tendency to become insensitive after one or two operations, and the necessityhof using an outside 'power source to energize the re alarm. It is the purpose of the present invention to obviate the foregoing and other difculties and disadvantages in the prior art by substituting a thermal detector which will not only signal the rise to a predetermined temperature -level but, of itself, will develop the electrical output to actuate the alarm, the detector operating on the principle of a primary cell. In this way, by combining the detecting means with the energizing means, not only is anV outside power supply eliminated but, in addition, a more direct and etiicient system is made available. Accordingly, it is a primary object of this invention to provide a lthermal detector which will accomplish the above mentioned advantages, is dependable in operation, and does not become impaired in sensitivity and accuracy for a reasonable number of operations.

It is another object to provide a system wherein the minimum operative temperature can be determined by the particular system ingredients selected.

Another object is to provide a system which will respond rapidly to the operative temperature to energize the lire alarm.

It is a further object to provide a thermal detector which is nonconductive up to the predetermined temperature level, and will return quickly to a nonconductive state upon a temperature reduction below the predetermined level.

A still further object is to providea lire alarm system which is liexible, rugged, inexpensive to manufacture and install, and which comprises a minimum number of parts. Accordingly, the system is' more readily conformable for 2,804,610 Patented Aug. 27, 1957 installation and detection in an increased number of selected locations and in practically any type configuration desired.

To accomplish the foregoing general objects, and other more specific objects which will hereinafter appear, the present invention will be more fully understood by reference to the following detailed description and drawings in which:

Figure 1 is a schematic view of a line type detector in the form of a continuous loop having an indicator electrically connected thereto.

Fig. 2 is a plan view, partly in section, of a line type detector in accordance with the invention.

Fig. 3 is a cross-sectional view of the invention taken on the lines 3 3 of Fig. l.

Fig. 4 is a right end view of the invention Fig. 2.

Fig. 5 is a schematic view of a continuous type detector in the form of a sheet, having an indicator electrically connected thereto.

Fig. 6 is a schematic view of a system having a hub and spoke arrangement, the indicator being the hub and the detector being the spokes.

Referring more particularly to the drawings, there is shown in Fig. l, a fire alarm system 10 having an elongated thermal electric cell or loop detector 11, and indicator l2 connected in electrical parallel relationship therewith. As shown in Figs. 2-4, the cell or detector 11 includes an outer tubular electrode 13 formed of a lirst metallic element, and an inner wire electrode 14 formed of a second dissimilar metallic element, the inner electrede being wrapped with an inorganic fibrous spacer material 15 which has been impregnated with a fused salt electrolyte, not separately shown.

As seen in Fig. l, the detector 11 may be flattened as in Fig. 3, then bent or twisted as desired to it the contour of any appropriate space or compartment 16 and eX- tended through a firewall 17 for electrical connection to the indicator 12. The indicator 12 may then be connected to an alarm 21 by means of a lead 18 connected across the two ends of the outer electrode 13, and a lead 19 connected across the two ends of the inner electrode 14; the leads 20 are then connected to fire alarm 21 with leads 1? and 19 thereby establishing an electrical parallel relationship between the detector 11 and lire alarm 21.

In my preferred embodiment, the outer electrode 13 is in the form of a nickel tube, the inner electrode 14 being in the form of an elongated magnesium strip. The fibrous spacer 15, of material such as glass or asbestos tape, is dipped into a bath of salt solution, such as an eutectic mixture of potassium and lithium chlorides with suitable depolarizers, for a sufficient time to allow the salt to impregnate the spacer and to solidify. The electrode 14 is then inserted into the spacer l5, the spacer and inner electrode combination in turn, being interposed within the outer electrode 13. The spacer and inner electrode combination are snugly engaged with one another and should tightly tit within the outer electrode. Other aspects of importance in the construction of the detector are, of course, that the inner and outer electrodes be formed of dissimilar metals, each of a substantially higher melting point than that of the electrolyte itself, and the composition of the electrolyte should be carefully regulated in proportions so that the initial melting of the insulating material will occur at the predetermined temperature level. At this level, the electrical conductance of the electrolyte will rapidly increase to establish an electrical circuit between the electrodes and to initiate an electrornotive force or voltage across the ends of the dissimilar metallic electrodes to the fire alarm.

lt is to be understood also that the spacer separating the shown in electrodes, although preferably of the composition above trolyte, when molten, to `wet both electrodes; however, it,Y has beenjfound that mypreferred embodiment ismnst` elfectivefin rapidly melting atthe .predeterminedlevely to energize the indicator, and subsequently upon cooling of the iire detector to .ret/urn to its n ormally solidcondition for-ming a sheath or'sleeve of high electrical resistance between the electrodes, *and further capable of repeated operations inthe event of additional temperature increases. Y Y

The simplicity and ease of making and installing the thermal-tdetector-and indicator make possible various configurations and adaptations of the device. As shown in Figures 2 and' 4,t-he circular thermal detector may be bent and/hor twisted into the desired shape, or may be flattened as in Figs; land 3. In--additiom the detector can be a loop as seen in Fig. l or can be straight with indicating means ati only one end as seen in Fig. 2^, or may have additional shapes with indicating means at either or both ends.

`In assembling the thermal detector 11 in Fig. 2, it is important that the detector assembly be hermetically sealed or insulated at the ends thereof to protect it and to prevent shorting between the electrodes.v Fig. 2 shows the detector 11 sealed at the end to which the indicator 12 is. to be connected by.means of a glass bead seal 21 having a conductive pin 23 extending therethrough, the pin 23 being electrically connected to the electrode 14. If desired, theV other end can also be hermetically sealed as described above, or by any one of the well known sealing means, such as by crimping as at 23. In utilizing either the glass bead seal 22 or the crimped portion 23, the inner electrode 14 is foreshortened somewhat for` placement of the yseal within the outer electrode to prevent electrical shorting between the electrode ends. The alarm device 21, which ist electrically connected to the conductive pin 2 3, or across the leads 20 may consist either of an electric lamp asshown in Fig. l, or an electric bell or buzzer system, andas shown in Figs. l and 2, a complete rupture occuring at any point along the detector as a resultof an. abnormal increase in temperature nevertheless will not impair the operability of that portion of the detector which is still in current conducting relationship` with the alarm.

Figs. V and 6 illustrate other possible configurations in combining the thermal detector and indicator: Fig. 5 shows an outer electrode plate 13a and inner electrode plate 14a, one or more indicators 12 being connected across the electrodes 13a and 14a at any point or points. In this form, the electrode 13a consists of a large bimetallic square Strip of nickel or other related metal, and the electrode 14a consists of a smaller dissimilar bimetallic square, preferably of magnesium juxtaposed with and spaced from the electrode 13a by means of a fused salt impregnated nonconductive spacer, not shown, thereby forming a detector in the form of a continuous sheet. In Fig. 6, the indicator 12 acts as the hub of the nre alarm system, the detectors 11b being the spokes, radiating therefrom in all directions, in either a two-directionalor a three-directional system. As shown, the detectors 11b are electrically connected in parallel, the indicator 12 being connected across the electrodes of the detector 11b.

Another important application of the invention is as an overheat alarm system for aircraft engine support i jacent surfaces of the two dissimilar metallic electrodes and causes an electrical current to be produced which serves to light the indicator lamp 11. Should the temperature of the. beam lst lbseqldlently fallpoflV below the fusion l point of the electrolyte, the V*electrolyte will solidify and current will no longer be produced. The light of the lamp will. be extinguish@ gs, an indication that the, temperature of the beam has been lowered to a safe level.

As various changes may be made in the form, construction, and arrangement Qt, the Parts herein described Without departing fttm the Spirit and scope, 0f the inverttion and without sacrificing any of the advantages, itis to be understood that all matter herein is to be interpreted as illustrative and not inlany limiting sense.

What i's claimed is: i

l. A lire alarm system comprising an elongated thermal electriccell-detector vhaving electrtical indicating means in current conducting vrelationship therewith, said detector*comprisingV an outer electrode of a first metallic element, an inner electrode of asecondrdissimilar metallic element, non'conductive spacing means disposed therebetween and fusible salt electrolyte interspersed with said spacer, -sadv electrolyte adapted' to melt at a predeterrninedtemperature and to cooperate with the electrodes to -produce"`a current adapted to actuate the indicating means.A

2. A fire alarm system comprising an elongated thermal electric cell, arid-electrical indicating means in current conducting relationship therewith, the thermal electric cell having a tubular electrode formed of a first metallic element, a wire electrode formed of a second dissimilar-metallic element, and a glass fiber tape spacer disposed therebetween and contiguous with the two electrodes, said tape being impregnated with a normally solid salt electrolyte, said* electrolyte adapted to melt at a predetermined temperature and to cooperate with the electrodes to produce a current adapted to actuateV the indica-ting means: 1 i

3. The' `inyention'cin accordanceV with claimr2 wherein the tubularouter electrode has been flattened and the inner-electrode has the form off an elongatedl strip.

^ 4. In; a tire alarm s ysternof the characterV described, a tubular outer electrode, a'at inner electrode disposed within said outer electrode, said electrodes being of dissimilar metal, a fibrous yspacerv element separating said electrodes, and an eutectic mixture of potassium and lithium. chloridesamll a depolarizerimpregnated in said spacer, saidV 'mixture adapted to melt at a predetermined temperature to cooperate with said electrodes to develop an electric potential.l i

5. An overheat system for aircraft engine support members, in which a thermal cell consists in a tubular outer electrode, an inner wire electrode of dissimilar metal, means to space` and to depolarize said electrodes, an eutectic salt electrolyte mixture impregnated in said Spacer t0. @streitet a. nredgtennned temperature land adapted t9 seguente-with Said slectrgdes t0 develop an electric potential, and means to insulate the ends of said electrodes. c

6, The system argentins to claim 5.1'11 which. Said cell iS Q f igdetgitg length,` zstegdily.- flexible, and adaptable t9 be bent-intensity@ Qonggratttm.-

7. A system of the character described, in which a thermal cell gogsists ig -g tubularenterv electrode, a wire ian' glggtr. d d' imitar ttltrtgl.,V an. inprganivbrous sp ser gtttlfsgid; glggtrodgs to.. ferm ,a Sheath of; high glggt insistance.ttigrglzetntga sa geestig-minute Qt potassium chlorides, lithium chloride, and a depolarizer impregnated in said spacer, said mixture adapted to melt at a predetermined temperature to cooperate with said electrodes to develop an electrical potential; a glass seal to insulate one end of said cell, and a crimped portion at the opposite end thereof to insulate said electrodes.

8. In a fire alarm system substantially as described, a flexible, thermal detector of continuous length comprising: an outer substantially tubular metallic electrode, an inner concentric electrode being of a second dissimilar metallic element from said outer electrode, a spacer including a exible brous wrapper of continuous length and an eutectic mixture of potassium chloride, lithium chloride and a depolarizer impregnated within said spacer, said spacer being interposed in close fitting relation between said inner and outer electrodes and extending continuously throughout the length thereof, said eutectic mixture adapted to melt at a predetermined temperature `level to develop an electrical potential between said elec- References Cited in the file of this patent UNITED STATES PATENTS Kitsee lune 4, 1907 Peters Feb. 19, 1952 

1. A FIRE ALARM SYSTEM COMPRISING AN ALONGATED THERMAL ELECTRIC CELL DETECTOR HAVING ELECTRICAL INDICATING MEANS IN CURRENT CONDUCTING RELATIONSHIP THEREWITH, SAID DETECTOR COMPRISING AN OUTER ELECTRODE OF A FIRST METALLIC ELEMENT, AN INNER ELECTRODE OF A SECOND DISSIMILAR METALLIC ELEMENT, NONCONDUCTIVE SPACING MEANS DISPOSED THEREBETWEEN AND A FUSIBLE SALT ELECTROLYTE INTERSPERSED WITH SAID SPACER, SAID ELECTROLYTE ADAPTED TO MELT AT A PREDETERMINED TEMPERATURE AND TO COOPERATE WITH THE ELECTORDES TO PRODUCE A CURRENT ADAPTED TO ACTUATE THE INDICATING MEANS. 